Chemistry: Post your doubts here!

[Student12]

Construct balanced equations for combustion for each of the first 4 alkanes and figure out how much volume you obtain. I'll do one of them to show you how it's like:

CH4 + 2O2 -> CO2 + 2H2O

10 cm^3 of CH3 will react with 20 cm^3 of oxygen, leaving 50 behind as residual gas. You also have 10 cm^3 of CO2, so thte total volume left is 60 cm^3.

You would also do this for the other alkanes, but since the only graph that starts with 60 cm^3 is D, you don't have to bother will the others.

I will do 11 and 14 later because they're quite long. #14 is mainly math though, just balance the equations for each metal and use ratio to figure out which one is the right answer.

Thank you so much ! i had been waiting for someone to reply my answer. I'll be waiting for 11 & 14
& please can you answer the other Question too, i had posted.

 

[hihi]

Hey does sum1 know how 2 solve this??
For 19..ans is D, for 20...CView attachment 8516

20) is 8 because 2^3(there are 3 double bonds) = 8

 

[thunderingthunder]

haha... this is again not a perfect reason... increase in pressure favours the side where there are less number of moles..
3H2 + N2 ---> 2NH3... reactants have 3+1 = 4 moles while products have only 2 moles.... so reaction proceeds to the side with less no of reacting moles...

I was refering to the question..the %age yeild increases because the forward reaction is favoured

 

[xxfarhaxx]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s07_qp_1.pdf
http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s07_ms_1.pdf
Q- 9,17,18,31,33

 

[umarashraf]

I was refering to the question..the %age yeild increases because the forward reaction is favoured

han han.. kar lo defend apnay aap ko...

 

[xxfarhaxx]

View attachment 8451
Hi please help me in this i cant figure out how to solve this.:/

is da ans D??

 

[umarashraf]

is da ans D??

yes.. it has to be D

 

[Student12]

There was an equillibrium Question i did the chemistry part.

0.0200= b/(1.00-b)
0.0200 x (1.00 - b ) =b
0.0200 - 0.0200 b = b
1.02 b = 0.0200
b = 0.0200 / 1.02
= 0.0196 mol

The above is the algebra part, can anyone explain me the 4th line how did 1.02 come from ?

 

[gary221]

Hey does sum1 know how 2 solve this??
For 19..ans is D, for 20...CView attachment 8516

hey guys...hw abt ques 19?? pls...
and this too...Ans is A

 

[xxfarhaxx]

yes.. it has to be D

if da ms sys da ans is D thn by lookin at it u cn tel..
cz nly iodine gves a yellow ppt!!

 

[hmlahori]

Can anyone explain this question?​

​

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_11.pdf​

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_er.pdf​

Q21 How does the compound have 5 double bonds. I counted 6(one in the side chain and 5 in the cyclohexene ring due to presense of just one hydrogen in it.)​

​

 

[xxfarhaxx]

hey guys...hw abt ques 19?? pls...
and this too...Ans is AView attachment 8518

Q 19..ans D.. c below

Q20. thr is a method to find ths..
fr any cis-trans.. 2^x
x= no. of double bonds
in ths question no of double bond is 3
thrfr 2^3=8, so C is da ans..

 

[xxfarhaxx]

hey guys...hw abt ques 19?? pls...
and this too...Ans is AView attachment 8518

Q 19 c below
Q 20.. fr any cis-trans 2^x (x=no.of doubl bnds) in ths cse it has 3 double bonds. thrfr 2^3=8.. ans C

 

[Zsiddiqui]

Need help for 6 questions of paper 1. The correct answer are circled.

 

[sumaiyarox:)]

y r tertiary alcohols resistent to oxidation?
how is the substitution reaction of an alcohol wit a hydrogen halide a nucleophilic substitution?cuz as far as i noe -nucleophiles are electron donors so wer is the donation of electrons taking place here??

 

[Executor]

Ok i dont mean to do spam or anything but please go to the following thread and make dua for all of us :
http://www.xtremepapers.com/community/threads/dua-for-all-candidates.14272/

Dont forget to share and Remember every share makes a difference

 

[gary221]

y r tertiary alcohols resistent to oxidation?
how is the substitution reaction of an alcohol wit a hydrogen halide a nucleophilic substitution?cuz as far as i noe -nucleophiles are electron donors so wer is the donation of electrons taking place here??

Did u try googling it??
nywy...The answer to this question depends on your point of view. From a thermodynamic point of view tertiary alcohols are resistant to oxidation, due to the fact that C-C single bonds are stable. Simply speaking, a carbon atom surrounded by three further carbon atoms and a C-O single bond will be more stable than a carbon atom surrounded by two carbon atoms and a C=O group. Quantum mechanical (ab-initio) calculations show that C-C single bonds are slightly electron donating with respect to each other, this means that the central carbon atom of a tertiary alcohol will be more stable than its oxidised analogue - therefore tertiary alcohols are resistant to oxidation under standard conditions.

One thing to note! Tertiary alcohols are only resistant to oxidation under standard conditions with mild oxidising agents - oxidation of tertiary alochols is possible, albeit under quite extreme conditions.

 

[Student12]

Q-6, 8, 9, 10, 18, 25, 35
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s10_qp_11.pdf
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s10_ms_11.pdf

i believe its the 3rd time i'm posting :/

 

[sumaiyarox:)]

Did u try googling it??
nywy...The answer to this question depends on your point of view. From a thermodynamic point of view tertiary alcohols are resistant to oxidation, due to the fact that C-C single bonds are stable. Simply speaking, a carbon atom surrounded by three further carbon atoms and a C-O single bond will be more stable than a carbon atom surrounded by two carbon atoms and a C=O group. Quantum mechanical (ab-initio) calculations show that C-C single bonds are slightly electron donating with respect to each other, this means that the central carbon atom of a tertiary alcohol will be more stable than its oxidised analogue - therefore tertiary alcohols are resistant to oxidation under standard conditions.

One thing to note! Tertiary alcohols are only resistant to oxidation under standard conditions with mild oxidising agents - oxidation of tertiary alochols is possible, albeit under quite extreme conditions.

thnxxxx....dat helped..
ps.nope i dint try googling it..!! ;P

 

[gary221]

how is the substitution reaction of an alcohol wit a hydrogen halide a nucleophilic substitution?cuz as far as i noe -nucleophiles are electron donors so wer is the donation of electrons taking place here??

its a nucleophilic substitution bcoz d C atom bonded to the hydroxyl grp will carry a partially positive charge (diff in electronegativity of O n C).
This makes it open to nucleophilic attack. ie the partially -ve halogen atom in hydrogen halide will attack the bond btw the C n hydroxyl grp..
Hope i helped!!